For the extraction of liquids and gases, such as oil, water and gas mixtures or the individual components thereof, from reservoir rock, well equipment is used, substantially comprising an extraction pipe for conducting the extraction medium from the outside extraction point to the inner extraction pipe. This may be a perforated pipe or a pipe which is provided with at least one opening. These openings are often provided with a suitable device, such as a slide or valve, with the aid of which the influence of the extraction medium can be controlled. This extraction pipe (inner pipe) is also referred to hereafter as a flow-through device; the terms sliding sleeve and sliding side door are also often used.
During extraction, it is necessary to separate the particles from the deposits and any particles artificially introduced or produced by abrasion from the extraction medium and to filter them out before entry into the extraction pipe.